Modern date and time handling in all Android versions (without sugar)

Modern date and time handling in all Android versions (without sugar)

Working with time in Android has always been tricky. People have been using either third party libraries (e.g. Joda-Time, ThreeTenBp) or had to work with the built-in time classes (such as Calendar). The built-in classes, although available in all Android versions, had a not-so-great API, were mutable (so not thread-safe), and timezone handling was a pain (ref).

In the latest Android Gradle plugin release (v.4.0.0+), "Java 8+ API desugaring support" was introduced. In plain language, we can use some Java 8 APIs and the plugin will translate those APIs to Android-compatible Java behind the scenes that can be used in all Android versions without requiring a minimum API level!

In general, Kotlin provides its Collections and Stream API replacements which are superior to Java's in my opinion. So from the list of Java 8 APIs, I think that only the excellent java.time API is interesting for a Kotlin developer. Finally, a nice date/time API that can be used in Android!

Note that this "desugaring" process might cost a few extra KB in your APK/AAB. But if that's not a deal-breaker for your case, you should consider using the newer APIs.

Set up

You would need to modify your build.gradle files. More details (and up-to-date version codes) in the official doc.

android {
  [...]

  defaultConfig {
    // Required when setting minSdkVersion to 20 or lower
    multiDexEnabled true
  }

  compileOptions {    
    // Flag to enable support for the new language APIs
    coreLibraryDesugaringEnabled true
    // Sets Java compatibility to Java 8
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
  }
  
  [...]
}



dependencies {
  [...]
  
  coreLibraryDesugaring 'com.android.tools:desugar_jdk_libs:1.0.9'
  
  [...]
}

Meet the classes

The time API is quite comprehensive and the complete exploration of the API is outside of the scope of this post. But, I want to introduce what I believe the main classes you probably going to need most of the time.

Instant

Instant is a point in time. Can be considered equivalent to a timestamp, if you are familiar with that term.

LocalTime, LocalDate, LocalDateTime

Each class represents the time, date, date+time respectively, without a timezone. Most people when thinking about date/time think in these terms anyway.

ZoneOffset, ZoneId

These are used to work with timezones. You would need one of those to convert a Local* to an Instant.

ZonedDateTime

You probably guessed it. This is what you get when combine a LocalDateTime with a ZoneId. This can be converted to an Instant.

Playing with date and time

These APIs provide intuitive and consistent ways to manipulate date and time. Remember that all objects are immutable, so a new object is created every time that a manipulation takes place (which is a good thing). Some useful examples follow.

val someDate = LocalDate.of(2020, 7, 28)
val someDateTime = LocalDateTime.ofEpochSecond(1595363833)
val someInstant = Instant.parse("2007-12-03T10:15:30.00Z")
Multiple ways to initialize time objects.
val today: LocalDate = LocalDate.now()
val startOfDay: LocalDateTime = today.atStartOfDay()
Get the start date+time of a day defined by a LocalDate
val now: LocalDateTime = LocalDateTime.now()
val nowInLA: ZonedDateTime = now.atZone(ZoneId.of("America/Los_Angeles"))
Get what date+time is now in Los Angeles.
val instant: Instant = nowInLA.toInstant()
val timestampInSeconds: Long = instant.epochSecond
val timestampInMilliseconds: Long = instant.toEpochMilli()
Get a point in time in various forms.
val today: LocalDate = LocalDate.now()
val previousWeek: LocalDate = LocalDate.now().minusWeeks(1)
Get the same day, 1 week earlier. There are available methods for every time unit.

Formatting

Just note that the formatters you are used to in Android, such as SimpleDateFormat, cannot be used with Java Time API. The API comes with its own formatters, such as DateTimeFormatter.

DateTimeFormatter.ISO_DATE.format(instant)

Enjoy a modern date/time API in your Android development life :)

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